5 - Plasma membranes Flashcards
What are the roles of membranes with a cell? (6)
Separates the cell’s components from its external environment.
Regulates the transport of minerals in and out via the partially permeable membrane.
Has antigens, so the organisms immune system recognizes it as not a threat.
May release chemicals that signal other cells.
Contain receptors for such chemical signals (hormones and drugs may bind to the receptors).
May be the site of chemical reactions.
The Fluid Mosaic Model
Theory of cell membrane structure with proteins embedded in a sea of phospholipids
Glycoprotein
…… attached to a …..
A carbohydrate chain attached to a protein molecule
Role in adhesion and as receptors for chemicals signals.
Intrinsic protein
EXAMPLES:
Receptors for the peptide hormones
Receptors for neurotransmitters
Glycolipid
…… attached to a …..
A carbohydrate chain attached to a lipid
Antigens
Cholesterol
A lipid with a hydrophobic and hydrophilic end.
Positioned between phospholipids and the bilayer.
Hydrophilic interaction with the head.
Hydrophobic interaction with the tail.
Cholesterol adds stability without making them to rigid
Prevents phospholipids form becoming solid and crystallizing
Phospholipid
…………………………
Intrinsic Proteins
Transmembrane proteins embedded through both layers of a membrane.
Channel Proteins
Provide a hydrophilic channels that allows the passive movement of molecules down a concentration gradient.
held in between the hydrophobic core and the hydrophobic R-group on the outside of the protein.
Carrier Proteins
Important role in active and passive transport.
This involves changing the shape of the protein
How does the temperature affect the membrane?
When temperature increases the kinetic energy increases so the phospholipids move more.
This makes the membrane more fluid and it begins to lose its structure
How do solvents affect the membrane?
Water is essential in the in the formation of phospholipid bilayer. The charged phosphate heads interact with the water keeping the bilayer intact.
Organic solvents will dissolve in membranes disrupting the cells. So alcohol is used in antiseptics to dissolve membranes of bacteria killing them.
Diffusion
Movement of molecules from an area of high concentration to a low concentration across a high concentration.
Facilitated diffusion
Movement of molecules from an area of high concentration to a low concentration across a high concentration across a partially permeable membrane via protein channels or carriers.
Why is diffusion a passive process?
They are described as passive processes as thy only use the kinetic energy of the cell and do NOT us ATP.
Factors affecting diffusion (3)
Temperature: as temp increase the KE increases, faster diffusion
Diffusion Distance: Thicker membrane, slower diffusion
Size of molecule: Smaller molecule, faster diffusion
Osmosis
A region where there is more water molecules to an area where there are fewer water molecules across a partially permeable membrane.
Water Potential
Pure water has the highest water potential of 0.
Solutes lower a water potential
Animals Cells Water Potential
A lot of water will swell the cell and burst = Cytolysis
Lower water potential —> less water in the cell = Crenated
Plant Cells Water Potential
Lots of water —> swollen cell = Turgid
Lower water potential —> less water in the cell —> cytoplasm shrinks membrane pulls away from the cell wall = Plasmolysed = Flaccid = Crenated
Active Transport
The movement of substances against their concentration energy across the concentration, using ATP and protein carriers.
Endocytosis
Bulk transport of molecules, too large to pass through the cell membrane, into the cell.
Exocytosis
Bulk transport of molecules, too large to pass through the cell membrane, out of the cell.
Bulk Transport
Some cells are too large to be transported in and out the membrane so they do this by bulk transport which requires ATP.
Effects of solvents on phospholipids
Organic solvents such as acetone will damage membranes as they dissolve lipids
Effects of the temperature on phospholipids
High Temperature - More KE —> permeability increases
Low Temperature - Saturated fatty acids becomes compressed - saturated fatty acids and unsaturated fatty acids maintain membrane fluidity
